1. Field of the Invention
The invention relates to the recycling of a platinum group metal, and more particularly to a method for preparing a solid ruthenium nitrosyl nitrate from a ruthenium-containing spent catalyst.
2. Description of the Related Art
There are two conventional methods for preparing ruthenium nitrosyl nitrate. One is to directly dissolve RuO4 in a cooled nitric acid solution, and the other is to dissolve and reflux nitrosyl ruthenium hydroxide in nitric acid.
In the first method, ruthenium hydroxide or RuO2.2H2O is mixed and stirred with micro-boiled nitric acid in a reflux device to yield a nitric acid solution of Ru(NO)(NO3)3. The nitric acid solution of Ru(NO)(NO3)3 has high acidity, and thus is difficult to store and transport.
In the second method, ruthenium trichloride and sodium nitrite react to yield an intermediate ruthenium nitrosyl chloride, which is then allowed to react with silver nitrate to yield a solution of ruthenium nitrosyl nitrate. The solution is extracted with ether and the ether extracts are evaporated to yield solid ruthenium nitrosyl nitrate. However, the method has the following disadvantages: 1. A chloride is involved, which poisons the catalyst; 2. The method involves the intermediate, thereby reducing the product yield; 3. ruthenium trichloride is used as crystalline hydrate, which is expensive.